Condensate water drain control system and method for fuel cells

ABSTRACT

A condensate water drain control system for fuel cells includes a fuel cell stack configured to generate electric power through chemical reaction, a fuel supply line configured to recirculate fuel discharged from the fuel cell stack together with fuel introduced from a fuel supply valve, a water trap located in the fuel supply line, the water trap being configured to collect condensate water discharged from the fuel cell stack, a drain valve configured to discharge the condensate water stored in the water trap to the outside when opened, and a drain controller configured to determine whether the fuel supply valve is controlled such that pressure in the fuel supply line is maintained before the drain valve is opened and to sense discharge of fuel from the fuel supply line through the drain valve upon determining that the pressure is maintained.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. § 119(a) the benefit of KoreanPatent Application No. 10-2020-0059600, filed on May 19, 2020 with theKorean Intellectual Property Office, the entire contents of which areincorporated by reference herein.

BACKGROUND 1. Technical Field

The present disclosure relates to a condensate water drain controlsystem and method for fuel cells, more particularly, to the condensatewater drain control system and method that are configured to sensehydrogen discharged from a hydrogen supply line by opening of a drainvalve.

2. Description of the Related Art

A fuel cell is a battery that directly converts chemical energygenerated as the result of oxidation of fuel into electrical energy, andthus serves as a type of power generation device. A fuel cell is similarto a chemical cell in that reduction-oxidation is used, but is differentfrom the chemical cell in that a reactant is continuously introducedfrom the outside and a reaction product is continuously discharged outof a system, unlike the chemical cell, which is configured such thatcell reaction occurs in a closed system. In recent years, a fuel cellgeneration system has been used practically, e.g., in a fuel cellvehicle, and research into using a fuel cell as an energy source forenvironmentally-friendly vehicles has been actively conducted, since areaction product from the fuel cell is pure water.

A fuel cell system includes a fuel cell stack configured to generateelectric energy through chemical reaction, an air supply deviceconfigured to supply air to an air electrode of the fuel cell stack, anda hydrogen supply device configured to supply hydrogen to a hydrogenelectrode of the fuel cell stack.

When electric power is generated in the fuel cell stack, water isgenerated in the fuel cell stack. Some of the water is discharged to thehydrogen electrode through an electrolyte membrane due to aconcentration difference. Hydrogen gas is recirculated to the hydrogensupply device through a recirculation device, and the water dischargedfrom the hydrogen electrode is condensed and is stored in a water trapincluded in the hydrogen supply device.

The water trap includes a water level sensor. When the level ofcondensate water sensed by the water level sensor is greater than orequal to a predetermined discharge level, a drain valve is opened todischarge the stored condensate water to the outside. In addition, whenthe level of condensate water sensed by the water level sensor isgreater than or equal to a predetermined interruption level, the drainvalve is closed to prevent the discharge of hydrogen.

In a case in which the water level sensor of the water trap breaks,however, it is not possible to measure the level of condensate waterstored in the water trap, whereby it is not possible to appropriatelycontrol the drain valve. In particular, when condensate water in thehydrogen supply device is not smoothly discharged to the outside, thewater generated in the fuel cell stack cannot be discharged to theoutside, whereby flow channels in a separator are blocked. If the drainvalve is opened more than necessary, hydrogen is unnecessarilydischarged, whereby fuel economy is deteriorated.

Conventionally, in order to solve this problem, fail-safe control isperformed to open the drain valve when, based on a current integrationvalue obtained by integrating current generated in the fuel cell stack,the current integration value reaches a predetermined value in the casein which the water level sensor of the water trap breaks. Since theamount of condensate water stored in the water trap is not uniformdepending on the state of the fuel cell stack, however, it is notpossible to accurately measure the level of the water trap.

To address this problem, a method of measuring the pressure in thehydrogen supply line in the state in which the drain valve is open isused. In the case in which target pressure in the hydrogen supply lineis variable in the state in which the drain valve is open, however, thedischarge of hydrogen is falsely detected despite hydrogen not beingdischarged from the hydrogen supply line.

The matters disclosed in this section are merely for enhancement ofunderstanding of the general background of the disclosure and should notbe taken as an acknowledgment or any form of suggestion that the mattersform the related art already known to a person skilled in the art.

SUMMARY

The present disclosure provides technology for accurately sensing thedischarge of hydrogen from a hydrogen supply line by opening of a drainvalve.

In accordance with an aspect of the present disclosure, the above andother objects can be accomplished by the provision of a condensate waterdrain control system for fuel cells, the condensate water drain controlsystem including a fuel cell stack configured to generate electric powerthrough chemical reaction in the fuel cell stack, a fuel supply lineconfigured to recirculate fuel discharged from the fuel cell stacktogether with fuel introduced from a fuel supply valve so as to besupplied to the fuel cell stack, a water trap located in the fuel supplyline, the water trap being configured to collect condensate waterdischarged from the fuel cell stack, a drain valve located in an outletof the water trap, the drain valve being configured to discharge thecondensate water stored in the water trap to the outside when opened,and a drain controller configured to determine whether the fuel supplyvalve is controlled such that pressure in the fuel supply line ismaintained before the drain valve is opened and to sense discharge offuel from the fuel supply line through the drain valve upon determiningthat the pressure is maintained.

The drain controller may determine whether the fuel supply valve iscontrolled such that the pressure in the fuel supply line is maintainedbased on a change in pressure in the fuel supply line or a change inopening degree of the fuel supply valve in the state in which the drainvalve is closed.

The condensate water drain control system may further include a pressuresensor configured to sense the pressure in the fuel supply line, whereinthe drain controller may determine whether the fuel supply valve iscontrolled such that the pressure in the fuel supply line is maintainedbased on a change in a pressure signal sensed by the pressure sensor.

The condensate water drain control system may further include a fueltank configured to store fuel in the fuel tank and a fuel supplycontroller configured to control the opening degree of the fuel supplyvalve such that the pressure in the fuel supply line follows a targetpressure, wherein the drain controller may determine whether the fuelsupply valve is controlled such that the pressure in the fuel supplyline is maintained based on a change in a signal for controlling theopening degree of the fuel supply valve from the fuel supply controller.

The fuel supply controller may fix the target pressure in the fuelsupply line in the case in which opening of the drain valve is required.

The condensate water drain control system may further include a powercontroller configured to fix required current or required power of thefuel cell stack in the case in which opening of the drain valve isrequired.

The condensate water drain control system may further include a batteryconfigured to be assist generation of electric power by the fuel cellstack while being charged or discharged by electric power generated bythe fuel cell stack and a load connected to the fuel cell stack and thebattery to receive electric power from the fuel cell stack or thebattery, wherein the power controller may control the required currentor required power of the fuel cell stack based on required power of theload or a charge amount of the battery, and may control charging anddischarging of the battery in order to satisfy the required power of theload in the case in which the required current or required power of thefuel cell stack is fixed.

The drain controller may sense the discharge of fuel from the fuelsupply line through the drain valve based on a change in pressure in thefuel supply line or a change in opening degree of the fuel supply valvein the state in which the drain valve is open.

The drain valve may be configured to have a purge function of purgingfuel in the fuel supply line to the outside when opened, and the draincontroller may measure a purge time from the point in time when thedischarge of fuel from the fuel supply line through the drain valve issensed to the point in time when the drain valve is closed.

The condensate water drain control system may further include aconcentration estimator configured to estimate an amount purged byopening of the drain valve and to estimate concentration of fuel in thefuel supply line through reflection of the estimated purge amount.

In accordance with another aspect of the present disclosure, there isprovided a condensate water drain control system for fuel cells, thecondensate water drain control system including a fuel cell stackconfigured to generate electric power through chemical reaction in thefuel cell stack, a fuel supply line configured to recirculate fueldischarged from the fuel cell stack together with fuel introduced from afuel supply valve so as to be supplied to the fuel cell stack, a watertrap located in the fuel supply line, the water trap being configured tocollect condensate water discharged from the fuel cell stack, a drainvalve located in an outlet of the water trap, the drain valve beingconfigured to discharge the condensate water stored in the water trap tothe outside when opened, a drain controller configured to sense thedischarge of fuel from the fuel supply line through the drain valve, anda fuel supply controller configured to control the fuel supply valvesuch that pressure in the fuel supply line is maintained when the drainvalve is opened under control of the drain controller.

In accordance with a further aspect of the present disclosure, there isprovided a condensate water drain control method for fuel cells, thecondensate water drain control method including: determining, by a draincontroller, whether a fuel supply valve is controlled such that pressureis maintained in a fuel supply line, which is configured to recirculatefuel discharged from a fuel cell stack together with fuel introducedfrom the fuel supply valve so as to be supplied to the fuel cell stack;opening, by the drain controller, a drain valve located in an outlet ofa water trap located in the fuel supply line, the water trap beingconfigured to collect condensate water discharged from the fuel cellstack, the drain valve being configured to discharge condensate waterstored in the water trap to an outside when opened; and sensing, by thedrain controller, discharge of fuel from the fuel supply line throughthe drain valve upon determining in the determining step that thepressure is maintained.

The step of determining whether the fuel supply valve is controlled suchthat the pressure in the fuel supply line is maintained may includedetermining whether the fuel supply valve is controlled such that thepressure in the fuel supply line is maintained based on a change inpressure in the fuel supply line or a change in opening degree of thefuel supply valve in the state in which the drain valve is closed.

The condensate water drain control method may further includedetermining whether opening of the drain valve is required before thestep of determining whether the fuel supply valve is controlled suchthat the pressure in the fuel supply line is maintained and fixing atarget pressure in the fuel supply line or fixing required current orrequired power of the fuel cell stack upon determining that opening ofthe drain valve is required.

The condensate water drain control method may further include measuringa purge time from the point in time when the discharge of fuel from thefuel supply line through the drain valve is sensed to the point in timewhen the drain valve is closed after the step of sensing the dischargeof fuel, estimating an amount purged by opening of the drain valve basedon the measured purge time, and estimating concentration of fuel in thefuel supply line through reflection of the estimated purge amount.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view showing the construction of a condensate water draincontrol system for fuel cells according to an embodiment of the presentdisclosure;

FIG. 2 is a view showing conventional condensate water drain and fuelsupply control signals; and

FIG. 3 is a flowchart showing a condensate water drain control methodfor fuel cells according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Throughout the specification, unless explicitly describedto the contrary, the word “comprise” and variations such as “comprises”or “comprising” will be understood to imply the inclusion of statedelements but not the exclusion of any other elements. In addition, theterms “unit”, “-er”, “-or”, and “module” described in the specificationmean units for processing at least one function and operation, and canbe implemented by hardware components or software components andcombinations thereof.

Further, the control logic of the present disclosure may be embodied asnon-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor,controller or the like. Examples of computer readable media include, butare not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes,floppy disks, flash drives, smart cards and optical data storagedevices. The computer readable medium can also be distributed in networkcoupled computer systems so that the computer readable media is storedand executed in a distributed fashion, e.g., by a telematics server or aController Area Network (CAN).

Specific structural or functional descriptions of the embodiments of thepresent disclosure disclosed in this specification or this disclosureare given only for illustrating embodiments of the present disclosure.Embodiments of the present disclosure may be realized in various forms,and should not be interpreted to be limited to the embodiments of thepresent disclosure disclosed in this specification or this disclosure.

Since the embodiments of the present disclosure may be variouslymodified and may have various forms, specific embodiments will be shownin the drawings and will be described in detail in this specification orthis disclosure. However, the embodiments according to the concept ofthe present disclosure are not limited to such specific embodiments, andit should be understood that the present disclosure includes allalterations, equivalents, and substitutes that fall within the idea andtechnical scope of the present disclosure.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, corresponding elementsshould not be understood to be limited by these terms, which are usedonly to distinguish one element from another. For example, within thescope defined by the present disclosure, a first element may be referredto as a second element, and similarly, a second element may be referredto as a first element.

It will be understood that when a component is referred to as being“connected to” or “coupled to” another component, it may be directlyconnected to or coupled to the other component, or interveningcomponents may be present. In contrast, when a component is referred toas being “directly connected to” or “directly coupled to” anothercomponent, there are no intervening components present. Other terms thatdescribe the relationship between components, such as “between” and“directly between” or “adjacent to” and “directly adjacent to”, must beinterpreted in the same manner.

Reference will now be made in detail to the preferred embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

FIG. 1 is a view showing the construction of a condensate water draincontrol system for fuel cells according to an embodiment of the presentdisclosure.

Referring to FIG. 1, the condensate water drain control system for fuelcells according to the embodiment of the present disclosure includes afuel cell stack 10 configured to generate electric power throughchemical reaction in the fuel cell stack 10, a fuel supply line 20configured to recirculate fuel discharged from the fuel cell stack 10together with fuel introduced from a fuel supply valve 42 so as to besupplied to the fuel cell stack 10, a water trap 30 located in the fuelsupply line 20, the water trap 30 being configured to collect condensatewater discharged from the fuel cell stack 10, a drain valve 32 locatedin an outlet 31 of the water trap 30, the drain valve 32 beingconfigured to discharge the condensate water stored in the water trap 30to the outside when opened, and a drain controller 50 configured todetermine whether the fuel supply valve 42 is controlled such that thepressure in the fuel supply line 20 is maintained before the drain valve32 is opened and to sense the discharge of fuel from the fuel supplyline 20 through the drain valve 32 upon determining that the pressure ofthe fuel supply line 20 is maintained.

The fuel cell stack 10 receives air including hydrogen and oxygen, asfuel, from a hydrogen electrode (anode) and an oxygen electrode(cathode), and generates electric power through chemical reaction. Inthe fuel cell stack 10, hydrogen and oxygen react with each other,whereby condensate water is generated.

The fuel supply line 20 supplies fuel from a fuel tank 41 to the fuelcell stack 10 and supplies fuel discharged from the fuel cell stack 10to the fuel cell stack 10 through recirculation. That is, fueldischarged from the fuel cell stack 10 is supplied to the fuel cellstack 10 through recirculation in the state of being mixed with fuelsupplied from the fuel tank 41.

The water trap 30 is provided in the fuel supply line 20 to storecondensate water generated in the fuel cell stack 10. In particular,condensate water generated by the oxygen electrode of the fuel cellstack 10 and moved to the fuel supply line 20 as the result of diffusionto the hydrogen electrode is collected and stored in the water trap 30.The outlet 31 of the water trap 30 may be connected to the outside, ormay be to a humidifier located in an oxygen electrode inlet of the fuelcell stack 10 in order to supply moisture.

The drain valve 32 may be provided in the outlet 31 of the water trap 30to control the discharge of condensate water from the water trap 30. Inparticular, the drain valve 32 may allow the discharge of condensatewater stored in the water trap 30 when opened, and may block thedischarge of condensate water when closed.

In general, the drain valve 32 is controlled to be closed such thathydrogen is not discharged through the outlet 31 of the water trap 30,and is opened to discharge condensate water to the outside when thecondensate water is intermittently stored.

The drain controller 50 may control opening and closing of the drainvalve 32. In particular, the drain controller 50 may sense or predictthe level of condensate water stored in the water trap 30, may performcontrol such that the drain valve 32 is opened in the state in which thelevel of condensate water is high, and perform control such that thedrain valve 32 is closed when the level of condensate water is loweredas the result of opening of the drain valve 32.

FIG. 2 is a view showing conventional condensate water drain and fuelsupply control signals.

Referring further to FIG. 2, conventionally, the water trap 30 includesa water level sensor 33 configured to sense the amount of condensatewater stored in the water trap 30, and opening and closing of the drainvalve 32 are controlled using the water level sensor 33.

In particular, when the storage amount of condensate water sensed by thewater level sensor 33 is greater than or equal to a predeterminedhigh-level critical value, the drain valve 32 is controlled to beopened, and when the storage amount of condensate water is less than orequal to a predetermined low-level critical value, the drain valve 32 iscontrolled to be closed.

However, the water level sensor 33 frequently malfunctions, wherebysensing accuracy is low and responsiveness is slow. As in an abnormaldischarge state of FIG. 2, therefore, the drain valve 32 remains open,whereby hydrogen is discharged through the outlet 31, even when thedischarge of condensate water is completed.

Conventionally, in order to solve this, control is performed such thatthe drain valve 32 is opened whenever the integrated value of outputcurrent of the fuel cell at the time of malfunction of the water levelsensor 33 reaches a predetermined integrated current value, ismaintained open for a predetermined opening time, and is then closed.However, opening and closing of the drain valve 32 are controlledirrespective of the amount of condensate water stored in the water trap30, which causes the discharge of hydrogen or flooding of the fuel cellstack 10.

In order to estimate the amount of condensate water stored in the watertrap 30 and to perform control based thereon even at the time ofbreakdown of the water level sensor 33, the drain controller 50 senseswhether fuel is discharged from the fuel supply line 20 through theoutlet 31 in the state in which the drain valve 32 is open, and performscontrol such that the drain valve 32 is closed upon sensing thedischarge of fuel.

In particular, the fuel supply valve 42 controls the pressure in thefuel supply line 20 so as to follow target pressure (PI control), andthe drain controller 50 senses the discharge of fuel through the outlet31 based on a signal for controlling the opening degree of the fuelsupply valve 42 in the state in which the drain valve 32 is open.

However, in the case in which such control is followed, as shown in FIG.2, when the target pressure in the fuel supply line 20 is changed in thestate in which the drain valve 32 is open, the pressure in the fuelsupply line 20 and the control signal of the fuel supply valve 42 arevariable, whereby fuel is misjudged to be discharged even in the case inwhich no fuel is discharged through the drain valve 32 (false detectionof hydrogen discharge state).

According to the present disclosure, in order to solve this problem, thedrain controller 50 may determine whether the fuel supply valve 42 iscontrolled such that the pressure in the fuel supply line 20 ismaintained when the drain valve 32 is opened, and upon determining thatthe fuel supply valve is controlled such that the pressure of the fuelsupply line is maintained, may sense the discharge of fuel from the fuelsupply line 20 through the drain valve 32 in the state in which thedrain valve 32 is open.

Consequently, the drain controller 50 may accurately sense the dischargeof fuel through the drain valve 32 in the state in which the drain valve32 is open, and therefore it is possible to prevent misjudgment of fueldischarge due to a change in pressure in the fuel supply line 20 due toanother environmental change.

Here, that the fuel supply valve 42 is controlled such that the pressurein the fuel supply line 20 is maintained means that the fuel supplyvalve 42 is controlled such that the pressure in the fuel supply line 20is maintained except that the pressure in the fuel supply line 20 ischanged as the result of the discharge of fuel from the fuel supply line20 through the drain valve 32. That is, a change in pressure in the fuelsupply line 20 due to other factors is minimized in the state in whichthe drain valve 32 is open.

In particular, the drain controller 50 may determine whether the fuelsupply valve 42 is controlled such that the pressure in the fuel supplyline 20 is maintained based on a change in pressure in the fuel supplyline 20 or a change in opening degree of the fuel supply valve 42 in thestate in which the drain valve 32 is closed.

In an embodiment, a pressure sensor 21 configured to sense the pressurein the fuel supply line 20 may be further included, and the draincontroller 50 may determine whether the fuel supply valve 42 iscontrolled such that the pressure in the fuel supply line 20 ismaintained based on a change in a pressure signal sensed by the pressuresensor 21.

In particular, the pressure sensor 21 may be located in the fuel supplyline 20 at the inlet side of the fuel cell stack 10 and may sense thepressure in the fuel supply line 20, and a fuel supply controller 40, adescription of which will follow, may adjust the opening degree of thefuel supply valve 42 based on the pressure in the fuel supply line 20sensed by the pressure sensor 21.

In particular, the drain controller 50 may differentiate the pressuresignal sensed by the pressure sensor 21 or calculate variation (absolutevalue) from a previous sensing value, and may determine that the fuelsupply valve 42 is controlled such that the pressure in the fuel supplyline 20 is maintained in the case in which the calculated differentialvalue or variation is maintained within a predetermined range for aperiod of time greater than or equal to a predetermined maintenancetime.

In another embodiment, a fuel tank 41 configured to store fuel in thefuel tank 41 and a fuel supply controller 40 configured to control theopening degree of the fuel supply valve 42 such that the pressure in thefuel supply line 20 follows the target pressure may be further included,and the drain controller 50 may determine whether the fuel supply valve42 is controlled such that the pressure in the fuel supply line 20 ismaintained based on a change in a signal for controlling the openingdegree of the fuel supply valve 42 from the fuel supply controller 40.

The fuel tank 41 may store high-pressure hydrogen in the fuel tank 41,and may supply the stored hydrogen to the fuel supply line 20 throughthe fuel supply valve 42. In particular, the high-pressure hydrogenstored in the fuel tank 41 may be supplied to the fuel supply line 20after being decompressed.

The fuel supply controller 40 may control opening and closing of thefuel supply valve 42 based on the pressure in the fuel supply line 20,and the signal for controlling the opening degree of the fuel supplyvalve 42 may be output from the fuel supply controller 40.

In particular, the fuel supply controller 40 may control opening andclosing of the fuel supply valve 42 based on the target pressure in thefuel supply line 20 and the pressure and temperature in the fuel supplyline 20. That is, the signal for controlling the opening degree of thefuel supply valve 42 may be set based on the target pressure in the fuelsupply line 20 and the pressure and temperature in the fuel supply line20.

The drain controller 50 may differentiate the signal for controlling theopening degree of the fuel supply valve 42 from the fuel supplycontroller 40 or calculate variation (absolute value) from a previouscontrol value, and may determine that the fuel supply valve 42 iscontrolled such that the pressure in the fuel supply line 20 ismaintained in the case in which the calculated differential value orvariation is maintained within a predetermined range for a period oftime greater than or equal to a predetermined maintenance time.

Referring to FIG. 2, variation in a pressure signal of the fuel supplyline 20 is relatively small, whereby it is difficult to sense thedischarge of fuel through the drain valve 32; however, variation in acontrol signal of the fuel supply valve 42 is relatively large, wherebyit is possible to rapidly, accurately, and easily sense the discharge offuel.

In an embodiment, the fuel supply controller 40 may fix the targetpressure in the fuel supply line 20 in the case in which opening of thedrain valve 32 is required.

The fuel supply controller 40 may set the target pressure in the fuelsupply line 20 based on required current or required power of the fuelcell. Particularly, in the case in which opening of the drain valve 32is required, the fuel supply controller 40 may fix the target pressurein the fuel supply line 20 even though the required current or requiredpower of the fuel cell is variable.

In another embodiment, a power controller configured to fix the requiredcurrent or required power of the fuel cell in the case in which openingof the drain valve 32 is required may be further included.

The power controller may control the required current or required powerof the fuel cell based on required current or required power of a loadand the charge amount of a battery 80, a description of which willfollow. That is, the power controller may set the required current orrequired power of the fuel cell in order to satisfy the required currentof the load, which is changed in real time. However, the powercontroller may perform control such that the required current orrequired power of the fuel cell is fixed in the case in which opening ofthe drain valve 32 is required.

A battery 80 configured to assist generation of electric power by thefuel cell stack 10 while being charged or discharged by electric powergenerated by the fuel cell stack 10 and a load connected to the fuelcell stack 10 and the battery 80 to receive electric power from the fuelcell stack 10 or the battery 80 may be further included.

That is, the fuel cell stack 10 and the load may be connected to eachother via a main bus end, and the battery 80 may be connected to themain bus end in parallel. In particular, a high-voltage converter 81 maybe located between the main bus end and the battery 80, and the powercontroller may control the high-voltage converter 81 to control chargingand discharging of the battery 80.

The power controller may control the required current or required powerof the fuel cell based on the required power of the load or the chargeamount of the battery 80, and may control charging and discharging ofthe battery 80 in order to satisfy the required power of the load in thecase in which the required current or required power of the fuel cell isfixed.

That is, the power controller may satisfy the required power of the loadthrough charging and discharging of the battery 80 when the requiredpower of the load is variable in the case in which the required currentor required power of the fuel cell is fixed.

In particular, required power Pt of the load may be the sum of requiredpower Ps of the fuel cell stack 10 and auxiliary power Pb of the battery80.

Pt=Ps+Pb->Pb=Pt−Ps

On the assumption that voltage of the main bus end between the fuel cellstack and the load is V, discharge current Ib of the battery 80 is asfollows.

Ib=Pt/V−Is

Here, in the case in which required current Is of the fuel cell stack 10is fixed and the required power Pt of the load is variable, thedischarge current Ib of the battery 80 may be variable to satisfy therequired power Pt of the load.

Particularly, in the case in which Ib>0, which is the state in which thebattery 80 is discharged, the power controller may control voltage ofthe high-voltage converter 81 to be Vref=V+α such that the battery 80 isdischarged.

On the other hand, in the case in which Ib<0, which is the state inwhich the battery 80 is charged, the power controller may controlvoltage of the high-voltage converter 81 to be Vref=V−α such that thebattery 80 is charged.

The drain controller 50 may control opening of the drain valve 32 basedon the storage amount of condensate water sensed by the water levelsensor 33. For example, when the storage amount of condensate watersensed by the water level sensor 33 is greater than or equal to apredetermined high-level critical value, the drain controller maydetermine that opening of the drain valve 32 is required.

In addition, when the storage amount of condensate water sensed by thewater level sensor 33 is less than or equal to a predetermined low-levelcritical value, or when the discharge of fuel through the outlet 31 issensed in the state in which the drain valve 32 is open, the draincontroller 50 may perform control such that the drain valve 32 isclosed.

In particular, the drain controller 50 may sense the discharge of fuelfrom the fuel supply line 20 through the drain valve 32 based on achange in pressure in the fuel supply line 20 or a change in openingdegree of the fuel supply valve 42 in the state in which the drain valve32 is open.

The drain controller 50 may sense the discharge of fuel from the fuelsupply line 20 through the drain valve 32 based on a pressure signalsensed by the pressure sensor 21 or a signal for controlling the openingdegree of the fuel supply valve 42 output from the fuel supplycontroller 40.

In an embodiment, in the case in which a rate of change in the signalfor controlling the opening degree of the fuel supply valve 42 outputfrom the fuel supply controller 40 is greater than or equal to apredetermined rate of change, the drain controller 50 may sense thatfuel has been discharged.

In the case in which the rate of change over time in the signal forcontrolling the opening degree of the fuel supply valve 42 output fromthe fuel supply controller 40 is abruptly variable to greater than orequal to the predetermined rate of change, it may be determined that thepressure in the fuel supply line 20 is abruptly changed, and thereforeit may be determined that fuel has been discharged through the outlet31.

In another embodiment, in the case in which a difference between thesignal for controlling the opening degree of the fuel supply valve 42output from the fuel supply controller 40 and an output signal referencevalue based on a pre-mapped output signal map is greater than or equalto a predetermined error, it may be sensed that fuel has beendischarged.

In the pre-mapped output signal map, the output signal reference valuemay be pre-mapped based on the target pressure in the fuel supply line20 and the temperature in the fuel supply line 20, and in the case inwhich the difference between the output signal reference value based onthe pre-mapped output signal map and the signal for controlling theopening degree of the fuel supply valve 42 output from the fuel supplycontroller 40 is greater than or equal to the predetermined error, itmay be determined that the pressure in the fuel supply line 20 isabruptly changed, and therefore it may be determined that fuel has beendischarged through the outlet 31.

In another embodiment, it may be sensed that fuel has been discharged atan inflection point at which a peak is formed as the result of thesignal for controlling the opening degree of the fuel supply valve 42output from the fuel supply controller 40 being decreased and thenincreased.

In an embodiment, the drain valve 32 may be configured to have a purgefunction of purging fuel in the fuel supply line 20 to the outside whenthe drain valve 32 is opened. That is, the drain valve 32 may dischargecondensate water accumulated in the fuel supply line 20, andsimultaneously perform the function of a purge valve 70 capable ofpurging fuel including impurities that flow in the fuel supply line 20to the outside.

The drain controller 50 may measure a purge time from the point in timewhen the discharge of fuel from the fuel supply line 20 through thedrain valve 32 is sensed to the point in time when the drain valve 32 isclosed.

The drain controller 50 may measure a purge time for which gas includingfuel is discharged from the fuel supply line 20 through the outlet 31from the point in time when the discharge of fuel through the drainvalve 32 is sensed to the point in time when the drain valve 32 isclosed.

In another embodiment, the purge valve 70 may be separately located atthe fuel supply line 20 downstream of the fuel cell stack 10.

A concentration estimator 60 configured to estimate an amount purged byopening of the drain valve 32 and to estimate the concentration of fuelin the fuel supply line 20 through reflection of the estimated purgeamount may be further included.

The concentration estimator 60 may multiply a discharge rate over timeby purge time (time from the point in time when the discharge of fuelthrough the drain valve 32 is sensed to the point in time when the drainvalve 32 is closed) to estimate an amount purged by opening of the drainvalve 32.

In particular, the concentration estimator 60 may estimate theconcentration of fuel in the fuel supply line 20 in real time byreflecting the purge amount and crossover amount transmitted to an airsupply line due to diffusion in the initial concentration in the fuelsupply line 20.

In particular, the concentration of fuel in the fuel supply line 20 maybe estimated on the assumption that only nitrogen, hydrogen, and vaporare present in the fuel supply line 20 while having uniformconcentration throughout the fuel supply line 20, as expressed by thefollowing numerical formula.

$\mspace{20mu}{\frac{\text{?}}{\text{?}} = {1 - \frac{\text{?}}{\text{?}} - \frac{\text{?}}{\text{?}}}}$?indicates text missing or illegible when filed

Here, n

is the total amount of gases in the fuel supply line 20, n

is the amount of nitrogen, n

is the amount of vapor, and n

is the amount of hydrogen.

The concentration of fuel in the fuel supply line 20 may be estimated byreflecting the amount of nitrogen and the amount of vapor introducedthrough crossover, the amount of hydrogen discharged through crossover,the purge amount, and the discharge amount in the initial concentrationin the fuel supply line 20.

The total amount of gases n

in the fuel supply line 20 may be estimated from an abnormal gas stateequation using pressure P, volume V, and temperature T in the fuelsupply line 20, as expressed by the following numerical formula.

$\mspace{20mu}{\text{?} = {\frac{\text{?}}{RT}\lbrack{mol}\rbrack}}$?indicates text missing or illegible when filed

Here, R is a gas constant, 8.314 [J/mol K].

The amount of nitrogen and the amount of vapor may be estimated byadding (amount of nitrogen introduced through crossover/amount ofvapor−amount of nitrogen by purge/amount of vapor−amount of nitrogendischarged through outlet 31/amount of vapor) to the initial amountthrough integration over time, as expressed by the following numericalformula.

?[mol] ?indicates text missing or illegible when filed

The initial amount of nitrogen or vapor may be estimated based on thepre-mapped map by reflecting the operation stop time in the case inwhich the operation of the fuel cell is stopped and then resumed.

In particular, the crossover amount of gas may be calculated by applyingFick's law (law of diffusion) below. The diffusion rate of gas may beinversely proportional to the thickness of an electrolyte membrane ofthe fuel cell stack 10, and may be proportional to a difference inpartial pressure of gas between the anode and the cathode

$\frac{\overset{.}{m}}{A} = {{{- D}\frac{\partial c}{\partial x}} = {{- D}\frac{M}{RT}\frac{\partial P}{\partial x}}}$

Here,

is mass diffusivity of gas (g/s), A is diffusion area, D is a diffusioncoefficient of gas, x is diffusion distance, c is the concentration ofgas, R is a universal gas constant (8.314 J/mol K), P is the pressure ofgas, T is the temperature of gas, and M is a molar mass of gas (g/mol),which may be arranged as follows.

$\overset{.}{m} = {{{- D}\frac{M}{RT}\frac{\partial P}{\partial x}A} = {\overset{.}{n} \cdot M}}$$\overset{.}{n} = {{- D}\frac{1}{RT}\frac{\partial P}{\partial x}A}$

Here,

is diffusivity of gas (mol/s).

That is, the crossover amount of gas through the electrolyte membrane ofthe fuel cell stack 10 may be calculated by the following numericalformula.

$\overset{.}{n_{N\; 2\;\_\;{xo}}} = {\frac{D_{N\; 2}}{RT}\frac{P_{{Ca},{N\; 2}} - P_{{An},{N\; 2}}}{\delta}A}$

Here,

is diffusivity of nitrogen, P is pressure [kPa], R is a gas constant(8.314 [J/mol K]), T is temperature [K], D is a diffusion coefficient, Ais the area of the electrolyte membrane,

is the thickness of the electrolyte membrane,

is the partial pressure of nitrogen at the cathode of the fuel cell, and

is the partial pressure of nitrogen at the anode of the fuel cell.

$\overset{.}{n_{V\;\_\;{xo}}} = {\frac{D_{V}}{RT}\frac{P_{{Ca},V} - P_{{An},V}}{\delta}A}$

Here,

is diffusivity of vapor, P is pressure [kPa], R is a gas constant (8.314[J/mol K]), T is temperature [K], D is a diffusion coefficient, A is thearea of the electrolyte membrane,

is the thickness of the electrolyte membrane,

is the partial pressure of vapor at the cathode of the fuel cell, and

is the partial pressure of vapor at the anode of the fuel cell.

Reversely, hydrogen may cross over from the anode to the cathode of thefuel cell.

$\overset{.}{n_{H\; 2\_\;{xo}}} = {\frac{D_{H\; 2}}{RT}\frac{P_{{An},{H\; 2}} - P_{{{Ca}.H}\; 2}}{\delta}A}$

Here, n_(H)

_(2_xo) is diffusivity of hydrogen, P is pressure [kPa], R is a gasconstant (8.314 [J/mol K]), T is temperature [C], D is a diffusioncoefficient, A is the area of the electrolyte membrane,

is the thickness of the electrolyte membrane, P_(An,H2) is the partialpressure of vapor at the anode, and P_(Ca,H2) is the partial pressure ofvapor at the cathode.

In addition, diffusivity of gas may be proportional to a diffusioncoefficient of gas, and the diffusion coefficient of gas may be variabledepending on water content and temperature of the electrolyte membranelocated between the anode and the cathode of the fuel cell.

In order to improve accuracy, a value that is variable depending on thestate, such as the degree of degradation or temperature, of the fuelcell may be used as the diffusion coefficient D of gas although a fixedconstant value may be used as the diffusion coefficient D of gas. Inparticular, the diffusion coefficient D of gas may be calculated using avalue that is variable depending on water content and temperature of theelectrolyte membrane located between the anode and the cathode of thefuel cell. In addition, the diffusion coefficient D of gas may becalculated as a variable value depending on degradation of theelectrolyte membrane of the fuel cell stack 10.

The purge amount may be estimated by integrating, over time, a dischargerate over time or multiplying the discharge rate over time by purgetime.

The discharge rate over time n

_(purge) may be proportional to a difference between gas pressure P_(An)at the anode and external gas pressure P_(out). The external gaspressure P_(out) may be gas pressure at the cathode. A concretenumerical formula may be as follows.

?dt ?dt ?indicates text missing or illegible when filed

Here, C is a purge gain value, which may be set based on the openingdegree of the purge valve 70 at the time of purge.

As expressed by the following numerical formula, the discharge rate overtime may be proportional to a difference in pressure between the fuelsupply line 20 and the outside, and a discharge gain may be multipliedas a proportional constant. The discharge gain may be proportional tothe diameter or the area of the outlet 31 of the water trap 30.

$\frac{\overset{.}{m}}{A} = {{{- D}\frac{\partial c}{\partial x}} = {{- D}\frac{M}{RT}\frac{\partial P}{\partial x}}}$

Here,

is a discharge rate over time, Cd is a discharge gain,

is pressure in the fuel supply line 20, and

is external pressure.

In addition, the purge amount of each gas may be estimated bymultiplying the total purge amount by the concentration of each gas inthe fuel supply line 20.

Furthermore, control may be performed such that the concentration in thefuel supply line 20 follows target concentration using the concentrationof fuel in the fuel supply line 20 estimated by the concentrationestimator 60. In particular, the concentration of fuel in the fuelsupply line 20 may be adjusted by controlling opening of the purge valve70, controlling opening of the drain valve 32 having the purge function,or controlling the fuel supply valve 42.

Consequently, it is possible to prevent degradation of the fuel cellstack 10 due to a decrease in concentration of fuel in the fuel supplyline 20, whereby it is possible to improve durability and to prevent areduction in fuel efficiency due to excessive concentration of fuel.

In an exemplary embodiment of the present disclosure, the fuel supplycontroller 40, the drain controller 50, and the concentration estimator60 may be realized by a non-volatile memory (not shown) configured tostore an algorithm for controlling the operation of various elements ofa vehicle or data on software commands for executing the algorithm and aprocessor (not shown) configured to perform an operation, which will bedescribed below, using the data stored in the memory. Here, the memoryand the processor may be realized as individual chips. Alternatively,the memory and the processor may be realized as a single integratedchip. The processor may include one or more processors.

FIG. 3 is a flowchart showing a condensate water drain control methodfor fuel cells according to an embodiment of the present disclosure.

Referring to FIG. 3, the condensate water drain control method for fuelcells according to the embodiment of the present disclosure includes astep of determining whether the fuel supply valve 42 is controlled suchthat the pressure in the fuel supply line 20, configured to recirculatefuel discharged from the fuel cell stack 10 together with fuelintroduced from the fuel supply valve 42 so as to be supplied to thefuel cell stack 10, is maintained (S300), a step of opening the drainvalve 32, located in the outlet 31 of the water trap 30 located in thefuel supply line 20, the water trap being configured to collectcondensate water discharged from the fuel cell stack 10, the drain valvebeing configured to discharge the condensate water stored in the watertrap 30 to the outside when opened (S400), and a step of sensingdischarge of fuel from the fuel supply line 20 through the drain valve32 upon determining in the determination step (S300) that the pressureis maintained (S500).

In the step of determining whether the fuel supply valve 42 iscontrolled such that the pressure in the fuel supply line 20 ismaintained (S300), it may be determined whether the fuel supply valve 42is controlled such that the pressure in the fuel supply line 20 ismaintained based on a change in pressure in the fuel supply line 20 or achange in opening degree of the fuel supply valve 42 in the state inwhich the drain valve 32 is closed.

Before the step of determining whether the fuel supply valve 42 iscontrolled such that the pressure in the fuel supply line 20 ismaintained (S300), a step of determining whether opening of the drainvalve 32 is required (S100) and a step (S200) of fixing the targetpressure in the fuel supply line 20 (S210) or fixing the requiredcurrent or the required power of the fuel cell stack 10 (S220) upondetermining that opening of the drain valve 32 is required may befurther included.

After the step of sensing the discharge of fuel (S500), a step ofmeasuring a purge time from the point in time when the discharge of fuelfrom the fuel supply line 20 through the drain valve 32 is sensed to thepoint in time when the drain valve 32 is closed (S600), a step ofestimating an amount purged by opening of the drain valve 32 based onthe measured purge time (S700), and a step of estimating theconcentration of fuel in the fuel supply line 20 through reflection ofthe estimated purge amount (S800) may be further included.

A condensate water drain control system for fuel cells according toanother embodiment of the present disclosure may include a fuel cellstack 10 configured to generate electric power through chemical reactionin the fuel cell stack 10, a fuel supply line 20 configured torecirculate fuel discharged from the fuel cell stack 10 together withfuel introduced from a fuel supply valve 42 so as to be supplied to thefuel cell stack 10, a water trap 30 located in the fuel supply line 20,the water trap being configured to collect condensate water dischargedfrom the fuel cell stack 10, a drain valve 32 located in an outlet 31 ofthe water trap 30, the drain valve 32 being configured to discharge thecondensate water stored in the water trap 30 to the outside when opened,a drain controller 50 configured to sense the discharge of fuel from thefuel supply line 20 through the drain valve 32, and a fuel supplycontroller 40 configured to control the fuel supply valve 42 such thatthe pressure in the fuel supply line 20 is maintained when the drainvalve 32 is opened under control of the drain controller 50.

The drain controller 50 may perform control such that the drain valve 32is opened in the case in which discharge of condensate water stored inthe water trap 30 is required. That is, the drain valve 32 may be openedin the case in which opening of the drain valve 32 is required.

In addition, the drain controller 50 may sense the discharge of fuelfrom the fuel supply line 20 through the drain valve 32 in the state inwhich the drain valve 32 is open. In particular, the drain controller 50may sense the discharge of fuel from the fuel supply line 20 based on apressure signal sensed by a pressure sensor 21 or a signal forcontrolling the opening degree of the fuel supply valve 42 output fromthe fuel supply controller 40.

The fuel supply controller 40 may control the fuel supply valve 42 suchthat the pressure in the fuel supply line 20 is maintained while thedrain valve 32 is open or before the drain valve 32 is opened.

In particular, the fuel supply controller 40 may control the fuel supplyvalve 42 such that the pressure in the fuel supply line 20 is maintainedby fixing target pressure in the fuel supply line 20 or required currentor required power of the fuel cell stack 10 while the drain valve 32 isopen or before the drain valve 32 is opened.

As is apparent from the above description, the condensate water draincontrol system and method for fuel cells according to the presentdisclosure have the effect of minimizing the discharge of hydrogen fromthe water trap through the outlet caused due to inaccuracy and slowresponsiveness of the water level sensor.

In addition, the condensate water drain control system and method forfuel cells according to the present disclosure have the effect ofaccurately estimating the concentration of fuel in the fuel supply lineso as to be used for purge control, etc., thereby improving accuracy incontrolling the concentration of fuel in the fuel supply line, andpreventing unnecessary purge control, thereby improving fuel economy.

In addition, the condensate water drain control system and method forfuel cells according to the present disclosure have the effect ofperforming control such that the pressure in the fuel supply line isvariable in order to solve a problem in that the discharge of fuelthrough the drain valve is falsely detected, thereby accuratelyestimating the concentration of fuel in the fuel supply line and thusimproving durability.

Although the preferred embodiments of the present disclosure have beendescribed above with reference to the accompanying drawings, thoseskilled in the art will appreciate that the present disclosure can beimplemented in various other embodiments without changing the technicalideas or features thereof.

What is claimed is:
 1. A condensate water drain control system for fuelcells, the condensate water drain control system comprising: a fuel cellstack configured to generate electric power through chemical reaction inthe fuel cell stack; a fuel supply line configured to recirculate fueldischarged from the fuel cell stack together with fuel introduced from afuel supply valve so as to be supplied to the fuel cell stack; a watertrap located in the fuel supply line, the water trap being configured tocollect condensate water discharged from the fuel cell stack; a drainvalve located in an outlet of the water trap, the drain valve beingconfigured to discharge the condensate water stored in the water trap toan outside when opened; and a drain controller configured to determinewhether the fuel supply valve is controlled such that pressure in thefuel supply line is maintained before the drain valve is opened and tosense discharge of fuel from the fuel supply line through the drainvalve upon determining that the pressure is maintained.
 2. Thecondensate water drain control system according to claim 1, wherein thedrain controller determines whether the fuel supply valve is controlledsuch that the pressure in the fuel supply line is maintained based on achange in pressure in the fuel supply line or a change in opening degreeof the fuel supply valve in a state in which the drain valve is closed.3. The condensate water drain control system according to claim 2,further comprising: a pressure sensor configured to sense the pressurein the fuel supply line, wherein the drain controller determines whetherthe fuel supply valve is controlled such that the pressure in the fuelsupply line is maintained based on a change in a pressure signal sensedby the pressure sensor.
 4. The condensate water drain control systemaccording to claim 2, further comprising: a fuel tank configured tostore fuel in the fuel tank; and a fuel supply controller configured tocontrol the opening degree of the fuel supply valve such that thepressure in the fuel supply line follows a target pressure, wherein thedrain controller determines whether the fuel supply valve is controlledsuch that the pressure in the fuel supply line is maintained based on achange in a signal for controlling the opening degree of the fuel supplyvalve from the fuel supply controller.
 5. The condensate water draincontrol system according to claim 4, wherein the fuel supply controllerfixes the target pressure in the fuel supply line in a case in whichopening of the drain valve is required.
 6. The condensate water draincontrol system according to claim 1, further comprising a powercontroller configured to fix required current or required power of thefuel cell stack in a case in which opening of the drain valve isrequired.
 7. The condensate water drain control system according toclaim 6, further comprising: a battery configured to be assistgeneration of electric power by the fuel cell stack while being chargedor discharged by electric power generated by the fuel cell stack; and aload connected to the fuel cell stack and the battery to receiveelectric power from the fuel cell stack or the battery, wherein thepower controller controls the required current or required power of thefuel cell stack based on required power of the load or a charge amountof the battery, and controls charging and discharging of the battery inorder to satisfy the required power of the load in a case in which therequired current or required power of the fuel cell stack is fixed. 8.The condensate water drain control system according to claim 1, whereinthe drain controller senses the discharge of fuel from the fuel supplyline through the drain valve based on a change in pressure in the fuelsupply line or a change in opening degree of the fuel supply valve in astate in which the drain valve is open.
 9. The condensate water draincontrol system according to claim 1, wherein: the drain valve isconfigured to have a purge function of purging fuel in the fuel supplyline to the outside when opened, and the drain controller measures apurge time from a point in time when the discharge of fuel from the fuelsupply line through the drain valve is sensed to a point in time whenthe drain valve is closed.
 10. The condensate water drain control systemaccording to claim 1, further comprising a concentration estimatorconfigured to estimate an amount purged by opening of the drain valveand to estimate concentration of fuel in the fuel supply line throughreflection of the estimated purge amount.
 11. A condensate water draincontrol method for fuel cells, the condensate water drain control methodcomprising the steps of: determining, by a drain controller, whether afuel supply valve is controlled such that pressure is maintained in afuel supply line, which is configured to recirculate fuel dischargedfrom a fuel cell stack together with fuel introduced from the fuelsupply valve so as to be supplied to the fuel cell stack; opening, bythe drain controller, a drain valve located in an outlet of a water traplocated in the fuel supply line, the water trap being configured tocollect condensate water discharged from the fuel cell stack, the drainvalve being configured to discharge condensate water stored in the watertrap to an outside when opened; and sensing, by the drain controller,discharge of fuel from the fuel supply line through the drain valve upondetermining in the determining step that the pressure is maintained. 12.The condensate water drain control method according to claim 11, whereinthe step of determining whether the fuel supply valve is controlled suchthat the pressure in the fuel supply line is maintained comprisesdetermining whether the fuel supply valve is controlled such that thepressure in the fuel supply line is maintained based on a change inpressure in the fuel supply line or a change in opening degree of thefuel supply valve in a state in which the drain valve is closed.
 13. Thecondensate water drain control method according to claim 11, furthercomprising: determining whether opening of the drain valve is requiredbefore the step of determining whether the fuel supply valve iscontrolled such that the pressure in the fuel supply line is maintained;and fixing a target pressure in the fuel supply line or fixing requiredcurrent or required power of the fuel cell stack upon determining thatopening of the drain valve is required.
 14. The condensate water draincontrol method according to claim 11, further comprising: measuring apurge time from a point in time when the discharge of fuel from the fuelsupply line through the drain valve is sensed to a point in time whenthe drain valve is closed after the step of sensing the discharge offuel; estimating an amount purged by opening of the drain valve based onthe measured purge time; and estimating concentration of fuel in thefuel supply line through reflection of the estimated purge amount.
 15. Acondensate water drain control system for fuel cells, the condensatewater drain control system comprising: a fuel cell stack configured togenerate electric power through chemical reaction in the fuel cellstack; a fuel supply line configured to recirculate fuel discharged fromthe fuel cell stack together with fuel introduced from a fuel supplyvalve so as to be supplied to the fuel cell stack; a water trap locatedin the fuel supply line, the water trap being configured to collectcondensate water discharged from the fuel cell stack; a drain valvelocated in an outlet of the water trap, the drain valve being configuredto discharge the condensate water stored in the water trap to an outsidewhen opened; a drain controller configured to sense discharge of fuelfrom the fuel supply line through the drain valve; and a fuel supplycontroller configured to control the fuel supply valve such thatpressure in the fuel supply line is maintained when the drain valve isopened under control of the drain controller.